1. Field of the Invention
The present invention relates to a simulation method for visualizing in three dimensions the density of a jawbone at the contact area between the jawbone and the surface of an implant screw using a virtual implant screw and based on information about the density of the jawbone obtained through computed tomography (CT) and also relates to a computer readable medium therefor.
2. Description of the Related Art
For the case where damage to teeth is too serious to repair, surgery for substituting artificial teeth for damaged teeth has become common. For such surgery, an implant screw for supporting the artificial teeth must be inserted into the jawbone.
FIGS. 1A through 1G illustrate each step of implantation. In detail, in the case where a tooth is damaged due to damage as shown in FIG. 1A, an artificial tooth is implanted into the damaged region as follows. The gum in the damaged region is cut as shown in FIG. 1B, a region into which an implant screw is to be inserted is drilled to form a hole as shown in FIG. 1C, and the implant screw is inserted into the hole as shown in FIG. 1D. Then, the implanted region is left to allow the implant screw to firmly bind, or osseointegrate, with the jawbone as shown in FIG. 1E. Usually, osseointegration takes about six months for the maxilla and about three months for the mandible. When the implant screw has firmly bound to the jawbone, the gum on the top of the implanted region is separated as shown in FIG. 1F and then an artificial tooth is mounted on the implant screw.
However, if a dentist fails to insert the implant screw into an appropriate region in an accurate direction during the above surgery, the implant screw cannot satisfactorily support the artificial tooth or the inappropriately inserted implant screw may encroach on alveolar nerves, causing numbness. Thus, the most important step in implantation is to accurately assess the density of the jawbone in the vicinity of a desired implantation location. In particular, contact between the implant screw and a low-density area and particularly encroachment on the nerves in the jawbone should be avoided.
Success in implantation depends on how accurately a dental surgeon knows the jawbone quality of a patient. The current leading method in accurately ascertaining the jawbone quality is computed tomography (CT). CT is a process by which an object is scanned by X-ray in many directions and synthesized through computation, resulting in an image of intersection. At a dental surgery, during CT scanning, either the maxilla or the mandible is typically scanned in 1.0 -mm increments, resulting in about 45 image slices. FIG. 2 shows a three-dimensional reconstruction image of a mandible obtained by CT.
As shown in FIG. 2, the images provided by CT are at intersections perpendicular to the long axis of the cervical spine, and these images are not suitable for inspecting the contact area between the implant screw and the jawbone. This is why a reformatting technique is applied after the images have been scanned by CT. In general, the most prevalent reformatting orientation is coronal, or perpendicular to the ramus of the mandible, or jawbone. However, because the jawbone is arch-shaped, the actual reformatted images may not be parallel to each other. Also, images perpendicular to the jawbone as well as images perpendicular to the cervical spine are very helpful in examining an implant site. Unfortunately, images perpendicular to the jawbone do not display the density distribution of the jawbone in a three-dimensional view, so that an implant surgeon cannot fully observe the density of jawbone at the contact area between the implant screw and the jawbone.
Due to the complicated three-dimensional structure of the jawbone, it is difficult to accurately observe an implant site in the jawbone from only the intersection image perpendicular to the cervical spine. This is the reason why CT software for dentist's provides a function capable of viewing the jawbone at different angles. For example, as the most common function of the CT software, a user can obtain a vertical sectional image by only drawing a parabola on a desired region of a given intersection, the vertical image corresponding to the desired region. However, using only the planar intersection (tomographic) images in identifying the density of a jawbone having a three-dimensional structure is not suitable for precise implantation.